1. Field of the Invention
The present invention relates to image processing technology.
2. Description of the Prior Art
In converting a low-contrast-ratio image to a high-contrast-ratio image, conventionally, one function that extends the dynamic range of pixel values has been equally applied to the entire image, an area in a screen has been divided so that a dynamic range of a bright portion is further expanded, or an expansion map that determines required expansion ranges for respective locations has been created and used.
Such a conventional method is merely for appropriately expanding the dynamic range of the pixel value of a low-contrast-ratio image, and thus is not effective in reconstructing detailed information (detailed texture, detailed contrast variation, etc.) of an image that falls within the category of a high-contrast-ratio image, i.e. does not fall within the category of a low-contrast-ratio image.
Since the low-contrast-ratio image is in a state in which a major portion of the contrast component of the pixel values for the detailed information of the image is lost due to a contrast ratio that is limited compared to that of a high-contrast-ratio image, it is necessary to improve the image quality by restoring the lost contrast components in a process of converting the low-contrast-ratio image into the high-contrast-ratio image.